RFID is a technology for sending an electromagnetic wave from an interrogator (reader/writer) to an ID (IC) tag that is attached to an object to be identified, and reading or writing the ID information on the object to be identified in a contactless manner. RFID has been widely used in management and the like on inventory or history (traceability) of items, such as commercial goods, as an RFID system with integrated circuit (IC) tags attached to the items.
An RFID system includes an IC tag including an IC chip with a small antenna and a reader/writer for wirelessly communicating with the IC tag. The reader/writer has an antenna. The reader/writer sends power for driving the IC chip in the IC tag and interrogation data to the IC tag, and obtains response data from the IC tag within a range for receiving the power and interrogation data, i.e., in a region allowed for communication, via the antenna. As an aspect of the RFID system, an RFID system that connects a plurality of antennas to the reader/writer to enable communication with a plurality of IC tags has been generally known.
An RFID system that enables communication with a plurality of IC tags is disclosed in Published Unexamined Patent Application No. 2006-338120, for example. In the publication, the system is adapted to connect a plurality of loop antennas with an antenna selector that is connected with a reader/writer in order. A corresponding IC tag communicates with the reader/writer via the loop antenna that is connected with the antenna selector.
The invention disclosed in the publication has an antenna selector always connected with a reader/writer, requiring a reader/writer for each antenna selector. Therefore, when two or more commercial goods shelves are provided in a warehouse, for example, each shelf needs to have a set of an antenna selector and a reader/writer. As bigger warehouses with more number of commercial goods shelves are used, more readers/writers are required. As a reader/writer is relatively expensive, the expenditure for them is increased. Further, once a great number of the sets are settled, commercial goods data cannot be obtained from the commercial goods shelves by using other types of generally used reader/writer, because an antenna selector is always connected with a reader/writer. In other words, the settled system is less flexible. As the number of readers/writers increases, communication lines (wiring) between the readers/writers and the central control unit (host computer) become more complicated, increasing the expenditure for the wiring.